Electrolysis cell



1959 H. B. WILLIAMS EI'AL 2,913,387-

ELECTROLYSIS cw.

Filed June 27, 1957 2 sheets-sheet 1 CATHODE CATHODE L R R L O A m m ELm L L F E E G D I cAsm 6 l4 ANODE HERBERT B.WILLIAMS CHARLES H.v0nTESMAR JOHN RENNER INVENTOR. BY Zimwce XDM-MA ATTORN EY FIG.|

REFRACTORY CASING l5 SLOT 6 DIAPHAGM H. a. WILLIAMS L 2,913,387

Nov. 17, 1959 ELECTROLYSIS cm. k

2 Sheets-Sheet 2 Filed June 27, 1957 GATHODE HERBERT B.WILL|AMS CHARLESH.von TES JOHN RENNE INVENTOR. BY i wwq 210% ATTORNEY United StatesPatent ELECTROLYSIS CELL Herbert B. Williams, Rochester, N.Y., CharlesH. von Tesmar, Ashtabula, Ohio, and John Renner, Warners, N.Y.,assignors to National Distillers and (Zhernical Corporation, New York,N.Y., a corporation of Virginia Application June 27, 1957, Serial No.668,417

'5 Claims. (Cl. 204247) This invention relates to new and improvedelectrolytic cells for fused salts. More particularly, the inventionconcerns an improvement in cathode construction for electrolysis cells,whereby the cathode is provided with at least one slot adapted to permittransfer, passage, and removal from the cell of the molten metalcathodic products substantially out of contact with reactive gaseousanodic products.

This application is a continuation-in-part of Serial No. 504,144, filedApril 27, 1955, now abandoned.

When metals are produced by electrolysis of fused salts, the cells aredesigned such that there is a relatively short distance between thecathode and the anode. This critical distance is necessitated, to alarge extent, by the fact that fused salts and mixtures of fused saltsare relatively poor conductors of electric current as compared with, forexample, aqueous solutions of electrolytes. Even under the mostadvantageous conditions, however, the current efiiciency is not entirelysatisfactory. For instance, in a typical electrolytic cell wherein fusedsodium chloride undergoes decomposition to produce metallic sodium, theaverage current efliciency obtained is about 80%. This efficiency can besubstantially increased and other advantages realized by preventing therecombination of the cathodic products with the anodic products. In theelectrolysis of fused sodium chloride, for example, a number of seriousdifliculties are caused by the chemical recombination of sodium andchlorine.

The ordinary electrolytic cell is constructed with a metallic diaphragm,usually made of metal gauze or mesh, and positioned between theelectrodes. This diaphragm is intended to prevent recombination.However, its use requires that both the molten cathodic product, sodium,and the gaseous anodic product, chlorine, travel upwardly along theentire vertical length of the electrodes before these products pass outof the electrolytic zone. During this passage the electrolysis productsare separated only by the diaphragm and, thus, there is considerableopportunity for recombination. In electrolytic cells of ordinary design,there is also a continual accumulation of metallic sodium and calcium onthe cathode. This accumulated metal causes short circuits across thediaphragm and periodic replacements of the gauze diaphragm arenecessary.

It is an object of the present invention to provide an electrolytic cellstructure for the production of sodium and chlorine from fused sodiumchloride in which current efiiciency is substantially improved. It isanother object of the invention to provide a cell structure in which,after initial decomposition, chemical recombination of elemental sodiumand chlorine is substantially avoided by rapid removal of the metallicsodium from the zone in which decomposition is effected. It is a furtherobject of the invention to reduce operating temperatures of such anelectrolytic cell. This is also eifected by reducing the amount ofrecombination.

According to this invention, an improved design for electrolytic cellsfor producingsodium and chlorine from til 2,913,387 Patented Nov. 17,1959 proved design is embodied in a cathode having at least onecircumferential slot at a critical location in the electrolysis zone,coupled with a deflector shield for retaining and guiding liquidcathodic product out of and away from the electrolysis zone.

The cell used can be any one of the conventional type used in theelectrolysis of alkali metal salts and mixtures thereof with alkalineearth metal salts for the production of alkali metals, having an anodeand cathode or plurality thereof. In accordance with the invention, thecathode is provided with at least one slotted portion. It is possible toprovide a cathode with about three slotted. portions, but the use of asingle slotted portion is a. particularly preferred feature of thisinvention. It hasbeen found, for example, that the cathode structure isconsiderably weakened when too many slotted portions are employed,whereas the use of only a single slotted portion obviates thisstructural weakness. This arrangement offers the further advantage ofmaintaining a relatively large, uninterrupted vertical cathode surfacein uniformly close proximity to the anode which permits operation of thecell at a lower voltage. In addition, as the number of slots areincreased the economic advantage is lessened due to the high cost offabricating such an intricate structure. By carefully locating thesingle slotted portion on the cathode, sufficient amounts of the moltencathodic product are effectively removed from contact with the gaseousanodic products to avoid much of the recombination difficultiesencountered in the prior art electrolysis cells. Thus, it has been foundthat when the cathode is provided with a slotted portion located aboutone third of the distance up from the lower end of the cathode, the cellvoltage remains relatively constant over long periods of operation,while the total production of sodium from the cell is increased byamounts up to one percent. Diaphragm changes are also required much lessfrequently, and in actual operation the effective life of the diaphragmwas doubled. When more than one slotted portion is employed, it ispreferred that at least two of the slotted portions be located in thelower half of the cathode. Though it is preferred exception of contactwith vertical stiffening or supporting bars, the slotted portions neednot necessarily be continuously circumferential in a single plane. Whenmore than one slotted portion is employed, they may be arranged asdiscontinuous, slotted portions which are vertically spaced, coaxial,and parallel to each other.

It is of particular importance in the construction of the slot itselfthat the slotted portion slopes upwardly and away from the anode. It hasbeen determined in actual tests that the molten metallic sodium willthus flow upwardly through the slotted portion and to the outside of thecathode away from the anode. The slope should preferably be adjusted tothe optimum angle for maximum cathode product removal which has beendetermined to be approximately about 50 to 60 from the horizontal.

It is a further feature of this invention that the top inner surface ofthe slotted portion is constructed to facilitate channeling of thesodium into the slotted opening. This result is most convenientlyaccomplished by having a protruding portion, such as a protruding lip,at the top or upper edge of the opening. For instance, a projection ofapproximately 1 1" to /2" in size functions quite satisfactorily indirecting and channeling molten sodium into the slot and to the outsideof the cathode. A similar effect can be accomplished by offsetting theupper or top slot edge in relation to the lower slot edge. For example,the upper portion of the cathode might possess slot.

Another very important and additional novel feature of the invention isthe use of a metal deflector shield which causes the cathode product toflow up the cathode of the cathode to the collector without dilfusingthrough the bath, burning on the top of the cell or recombining with theanodic product. The deflector means are positioned between the cathodeand the inner wall of the electrolysis cell in close proximity to theoutside periphery of the cathode, so as to confine the sodium and directit upwardly into the collector, suspended above. The defiector meansmay, for example, be attached to the arm which holds the cathode inposition in the cell. Though the deflector means may extend the lengthof the cathode, it is only necessary that the deflector means extend toa point just below the lowest slot in the cathode to ensure the upwardchanneling of the cathodic product flowing through the slot.

The collecting means useful for the purposes of this invention may beany of the conventional types. It is preferred, however, that thecollecting means be located annularly around the gaseous anodic productcollecting dome and that it extend over the cathode assembly, includingthe deflector means. When a diaphragm is employed, it may convenientlybe attached directly to the inner wall of the collecting means andsuspended about mid-way in the annular space between the anode and thecathode. The diaphragm may be of the perforated, cylindrical steel type.

Numerous advantages result when the improved electrolysis cell of thisinvention is utilized. These advan tages are achieved principallybecause the construction substantially prevents direct contact betweenthe molten cathode product and the gaseous anode product. Morespecifically, the inventive electrolytic cell effectively preventscontact between molten sodium and gaseous chlorine in the electrolysisof fused sodiumchloride. Thus, the principal advantage is the avoidanceof chemical recombination between the anode and cathode products byremoving rapidly, and as formed, a substantial portion of the cathodeproduct from the area where recombination is most likely to occur. Thismaterially increases the cfiiciency of the cell and also has thebeneficial eilect of decreasing D e cell temperature which normally isincreased by the heat of the recombination reaction.

Upward passage of a large portion of the cathode product along theoutside of the cathode between the metal deflector and cathode, and itsrapid removal from the cell also reduces the amount of products whichdiffuse through the diaphragm between the electrodes. period ofusefulness of the diaphragm itself is, consequently, extended sincethere is less accumulation of materials between the cathode and thediaphragm thereby reducing the number or" short circuits. This isparticularly true for electrolytic cells wherein fused mixtures ofsodium and calcium salts are used as the electrolyte. At thetemperatures used in'the process some calcium metal is obtained as aby-product, and a portion of the calcium would ordinarily deposit on themetal diaphragm and form bridges which cause current losses and shortcircuits. Such short circuits substantially reduce the power efllciencyof the cell and cause localized overheating of portions of thediaphragm, materially shortening its useful life.

One method and type of apparatus for carrying out the invention isillustrated by the appended drawings. Figure l is a diagrammaticvertical sectional view of an electrolysis cell containing the cathodeassembly of this invention. Figure 2 is a horizontal cross sectionalview taken on the plane y-y of Figure 1, while Figure 3 is an enlargedview of a small section of the cathode and deflector assembly and showsthe slotted portion in greater detail.

Referring now to Fig. 1, there is shown a cylindrical electrolysis cellhaving an iron or steel cylindrical cell wall lined with refractorymaterial 13, a cylindrical graphite anode 5 projecting upwardly throughceramic The.

4 casing 14 from the bottom of the cell, and a steel cylindrical cathode3 positioned vertically coaxial with anode 5 and spaced apart therefrom.Cathode 3 has two diametrically opposed steel arms 4, which projectoutside of the cell, through ceramic insulating casing 15, to serve aselectrode terminals. The cell is also provided with a perforatedcylindrical steel diaphragm 8 attached to collector 9 and suspended inthe annular space between anode 5 and cathode 3. The annular collectorring 9 serves to support diaphragm 8 and to collect molten metal whichrises in the fused electrolyte from cathode 3. Outlet pipe 12 serves tocarry the molten metal accumulated in collector ring 9 away from thecell, while gas dome 11 serves to carry away the gaseous anodic productformed by electrolysis. Deflector shield 1 is a solid, continuousmetallic casing surrounding the cathode assembly, its principal functionbeing to prevent dispersion throughout the cell of globules of moltenmetal by guiding the molten metal upwardly into collector 9 and out ofthe cell. The metal deflector l is supported by cathode arms 4 and ispositioned in the annular space between refractory material l3 andcathode 3. Anode 5 and cathode arms 4 are insulated from direct contactwith cell wall 10 by refractory ceramic casings 14 and 15, respectively.

Cathode 3 is provided with a slotted portion 6, which is acircumferential opening located in the lower third of cathode 3. Theslot is sloped upwardly and away from the anode 5. The upper edge ofslotted portion 6 is provided with a protruding lip 7, extending aroundthe entire inner wall of cathode 3. In Figure 2 the protruding lip 7 isshown in relationship with other members of the electrolysis cell ofthis invention, while in Figure 3 the slotted portion and the protrudinglip are shown in greater detail in relationship to cathode 3 anddeflector 1. In a typical operation of the cell shown in Fig. 1, amixture of about 42 weight percent sodium chloride and 58 weight percentcalcium chloride is placed in the brick lined cell provided with theabove described upwardly projecting anode 5, slotted cathode 3,deflector shield 1 and a steel gauze diaphragm 8. Current is applied tothe electrodes with an average voltage of about 6 to 7 volts dependingon the amperage, which in turn is variable depending on the productionlevel desired. The temperature is approximately 600 C. which maintainsthe fused salt mixture in a molten state. As the sodium chloride iselectrolyzed, the chlorine collects at the anode and is passed upwardlyand out of the cell via gas dome 11. The principal portion of the moltensodium formed during electrolysis collects on the lower part of cathode3 on the inner side adjacent to anode 5. As the molten sodium starts tomove upwardly, its flow is interrupted by protruding lip 7, whichchannels substantially all of the molten sodium formed below the slottedportion through slot 6 to the outside of cathode 3. The molten sodium isthen directed upwardly through the annular space formed by metaldeflector 1 and the outside of cathode 3 into collector ring 9 and outof the cell via outlet pipe 12. Experience has shown that the greaterportion of the electrolysis products are formed in the lower third ofthe electrolytic zone, since a greater proportion of the current flowsthrough the lower resistance path. Thus, a considerable amount of themolten sodium formed during electrolysis is passed out of the cellsubstantially out of contact with the chlorine gas thereby preventingthe anodic and cathodic products from recombining.

While the principles of the invention have been described above withrespect to one particular form of electrolysis cell, it will beunderstood that equivalent forms of apparatus are also contemplated.Thus, cells embodying the slotted cathode may be constructed with aplurality of anodes each individually circumscribed by the inventivecathode assembly. It will be appreciated that the use of such cells willcall for modifications which l be within th p r e o hose k d n thread-One variance might involve the use of only one deflector shieldsurrounding the bank of anodes and cathodes. Such an arrangement wouldutilize in part the outside walls of the adjacent cathodes as means fordirecting a portion of the flow of the molten cathodic product, afterits passage through the slots, upwardly into the collector and out ofcontact with the gaseous anodic products. It will be understood,therefore, that other modifications and variations may be employedwithin the scope of the invention described above and the followingclaims.

What is claimed is:

1. A cell adapted for electrolysis of fused salts having a cylindricalvertical side Wall, at least one vertically disposed anode extendingupwardly from the bottom of said cell, a cylindrical, concentric cathodespaced apart from and surrounding said anode, collecting meanspositioned above said cathode and adapted to collect cathodic product,said cathode being provided with from one to three vertically spaced,coaxial, parallel and substantially circumferential slots, each of saidslots sloping upwardly away from said anode and having a protrudingportion at the upward edge of said slots on the inner wall of saidcathode, said protruding portion being adapted to channel cathodicproduct from below said slots through said slots and out of contact withanodic product, the remainder of said cathode being continuous,vertically disposed deflector means disposed between said cathode andinner Wall of said cell, said deflector means being spaced apart fromsaid cathode and said inner wall and adapted to channel cathodic productexiting from said slots upwardly and into said collecting means.

2. A cell according to claim 1 wherein said cathode is provided with oneslot, said slot being located in the lower portion of said cathode.

3. A cell according to claim 2 wherein said slot is located aboutone-third from the bottom of said cathode.

4. A cell according to claim 1 having a vertically disposed diaphragmbetween said cathode and said anode, said diaphragm being spaced apartfrom said cathode and said anode.

5. A cell according to claim 1 wherein said slots are sloped at an anglefrom about to from the horizontal.

References Cited in the file of this patent UNITED STATES PATENTS1,921,376 Ward Aug. 8, 1933 1,921,377 Ward Aug. 8, 1933 2,592,483 Smithet a1. Apr. 8, 1952

1. A CELL ADAPTED FOR ELECTROLYSIS OF FUSED SALTS HAVING A CYLINDRICALVERTICAL SIDE WALL, AT LEAST ONE VERTICALLY DISPOSED ANODE EXTENDINGUPWARDLY FROM THE BOTTOM OF SAID CELL, A CYLINDRICAL, CONCENTRIC CATHODESPACED APART FROM THE SURROUNDDING SAID ANODE, COLLECTING MEANSPOSITIONED ABOVE SAID CATHODE AND ADAPTED TO COLLECT CATHODIC PRODUCT,SAID CATHODE BEING PROVIDED WITH FROM ONE TO THREE VERTICALLY SPACED,COAXIAL, PARALLEL AND SUBSTANTIALLY CIRCUMFERENTIAL SLOTS, EACH OF SAIDSLOTS SLOPING UPWARDLY AWAY FROM SAID ANODE AND HAVING A PROTUDINGPORTION AT THE UPWARD EDGE OF SAID SLOTS ON THE INNER WALL OF SAIDCATHODE, SAID PROTUDING PORTION BEIN ADAPTED TO CHANNEL CATHODIC PRODUCTFROM BELOW SAID SLOTS THROUGH SAID SLOTS AND OUT TO CONTACT WITH ANODICPRODUCT, THE REMAINDER OF SAID CATHODE BEING CONTINUOUS, VERTICALLYDISPOSED DEFLECTOR MEANS DISPOSED BETWEEN SAID CATHODE AND INNER WALL OFSAID CELL, SAID DEFLECTOR MEANS BEING SPACED APART FROM SAID CATHODE ANDSAID INNER WALL AND ADAPTED TO CHANNEL CHTHODIC PRODUCT EXITING FROMSAID SLOTS UPWARDLY AND INTO SAID COLLECTING MEANS.